1. Field of the Invention
The present invention relates to a position detecting apparatus adapted for detecting the position appointed by a position appointing magnetism generator, upon sensing a change in the magnetic permeability of a magnetic body which takes place when a magnetic field is applied to the magnetic body by the position appointing magnetism generator.
2. Description of the Prior Art
A position detecting apparatus is known in which a magnetostrictive transmission medium is used in combination with a position appointing pen. In this apparatus, a driving coil is provided on one end of the magnetostrictive transmission medium or on the end of the position appointing pen, while a detecting coil is provided on the end of the position appointing pen or one end of the magnetostrictive transmission medium. In operation, a pulse current is supplied to the driving coil to generate a magnetostrictive vibration wave in the magnetostrictive transmission medium, and the time duration between the moment at which the magnetostrictive vibration wave is generated and the moment at which the voltage induced by the magnetostrictive vibration wave is detected by the detecting coil is measured and processed by a suitable processor, thus detecting the position appointed by the position appointing pen. This known position detecting apparatus permits a considerably high precision of position detection, but suffers from problems due to the necessity for a cord through which the pen and the processor are connected to each other for the exchange of timing signals. Specifically, the handling of the pen is inconveniently hindered by the presence of the cord. In addition, the cord tends to pick-up noises due to induction of voltage by the influence of other devices, often resulting in erroneous operation. The presence of the cord also affects other devices through generation of noises. It is to be pointed out also that the pen has to be maintained substantially normal to and in the close proximity of the magnetostrictive transmission medium.
Another known position detecting apparatus has a plurality of driving lines and a plurality of detecting lines which are arranged orthogonally to each other. In operation, electric current is supplied successively to the driving lines while the detecting lines are scanned for the detection of voltage induced in one of the detecting lines when approached by a position appointing pen having a magnetic body such as ferrite. This apparatus does not require any cord for connecting the pen to the stationary part of the apparatus so that most of the problems encountered by the first-mentioned apparatus are overcome. In this apparatus, however, the resolution of the coordinate positions is determined by the pitches of the lines. It is quite difficult to attain high resolution through arranging the lines at small pitches because such small pitches impose other problems such as poor S/N ratio and low stability of operation. In addition, it is quite difficult with this apparatus to detect positions which are on the points of intersection between the driving lines and detecting lines. Furthermore, since the position appointing pen must be used in the close proximity of the lines, it is impossible to appoint the position through the intermediary of a thick structure placed on the tablet formed by the driving and detecting lines.